For years, the central axiom of modern campaigning has been that elections are won and lost on television. So, it must say something about the state of American politics that fewer people than ever are expected to watch this summer's two party conventions on television than ever before.

It is also ironic that America's national television networks are busy scaling down their coverage of the upcoming conventions to the lowest in years.

Four years ago in San Diego, the Republicans ran a slick, controlled convention from which every possible negative image was ruthlessly expunged. Journalists began moaning that what had once been a fibrous and newsworthy part of the political process was being turned into an "infomercial". The ABC network anchor Ted Koppel even pulled out of San Diego after two days in protest, taking his crew with him.

When the Republicans gather in Philadelphia on July 31 for their 2000 convention, the television networks will be back. But only just.

Until this week, when they were forced to change their plans, ABC had been intending to cover the opening night of the convention only in the halftime interval of a pre-season American football game, with longer reports on the other three nights. CBS, which had been planning to cover just two of the four nights at Philadelphia, said on Monday that it now intends to offer at least some coverage every night.

But the bottom line in Philadelphia - and in the August 14-17 Democratic convention in Los Angeles too - is that things ain't what they used to be. In the 1970s, the networks were there every night offering extensive live coverage. In 1976, a peak year, the conventions had a combined rating of 35. points, meaning that 35 per cent of all American households were watching the conventions in an average broadcasting minute.

By 1996, the rating was down to 24 points, the lowest yet recorded. The average family watched less than four hours during the two conventions last time round. No one expects that record to survive the 2000 convention season.

Part of the reason for the likely slump this year is the revolution in television news. While the networks stay away, or scale down their coverage, their cable subsidiaries and their competitors are actually increasing their broadcast hours. MSNBC will in effect take over political coverage from its parent NBC. CNN will offer nearly 100 hours coverage from each of the conventions.

But the mathematics of such flexibility points steadily downwards. CNN may hope to put 10 per cent on its audiences in convention weeks, but the cutbacks on the networks - which reach many more households than the cable channels do - mean that the overall numbers of convention viewers will be the smallest ever.

This decline is matched by a downturn in interest. Harvard university's Kennedy School of Government reported this week that 43 per cent of voters in a poll for their "Vanishing Voter Project" said they did not plan to watch any of the Republican convention, while 38 per cent didn't expect to tune in to the Democrats. Four years ago - when the record low was set - the corresponding figures were 23 per cent and 21 per cent.

One significant consequence is that both parties will feel driven to compensate by buying more advertising time. To pay for the increase in slots, the campaigns will have to raise even more money, including the "soft money" that so many people feel is debauching the electoral process. The break-up of the old media monopolies is increasing the power of the rich donors, another paradox.

The parties have invested a lot of time and muscle in trying to get more coverage for their conventions. The changes of heart by both ABC and CBS about their coverage only came after the Democrats scheduled Bill Clinton for an opening night address in LA, forcing the networks to cover the president and compelling them - on grounds of balance - to also cover General Colin Powell's opening night speech to the Republicans.

But the parties also know that the process of change is irreversible, and they are adapting to it. Both the conventions will be available live on the internet, as the parties try to reach out to more voters. The Republicans are inviting net surfers to become "dot.com delegates", while the Democrats are promising "E-mersion coverage".

From a media point of view, coverage of the 2000 conventions will be the most innovative yet. But the sober fact, in spite of all the new media, is that viewing will slump overall. It is not surprising that most forecasters think that, come election day on November 7, this lack of contact will ultimately mean that fewer people will vote this year than in any presidential election on record.